I'm not used to the 8 being bracketted, although I have see it as 8ve. For higher ranges than the treble clef, the 8 can be above the clef indicating that the notes are peformed an octave higher than written. As mentioned above, on most 4 stave SATB choral music, the tenor line is usually written on the treble clef, but sung an octave lower - as a tenor I dislike having my part written on a bass clef.